In recent years, various image sensing modules have been developed each of which contains a compact digital camera or a compact digital video unit each including a solid-state image sensing device that includes a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor). Since, in particular, portable information terminals and mobile telephones are now in widespread use, there is a demand that such portable information terminals and mobile telephones should each include an image sensing module which is compact and which has a reduced height and a great resolving power.
An image sensing lens including four lenses, which is compact and which has good optical characteristics, has been drawing attention as an image sensing lens that can meet the above demand.
The image sensing lens including four lenses has a lot of applications which range from a module including a 5M (mega)-class sensor to a camera module (image sensing module) having a large number of pixels. Such a camera module particularly has a larger number of pixels and is smaller in height recently. This trend will continue to increase the demand for the above image sensing lens for use in a camera module having a large number of pixels.
The image sensing lens, which is mounted in a middle-class to high-end model camera, will mostly be (i) a “4P” lens, that is, a lens including four plastic lenses, or (ii) a “1G3P” lens, that is, a lens including one glass lens and three plastic lenses. This is because the above image sensing lens, if including more or fewer than four lenses, will be difficult to produce in terms of its production cost and size.
It is true that 1G3P lenses seem to be a promising option in view of good optical characteristics of a glass material. There is, however, concern about an increase in cost and a decrease in productivity in a case where a glass material is used. Thus, 1G3P lenses will be used for only limited models. The image sensing lens including four lenses will therefore be a 4P lens for most applications.
Patent Literatures 1 through 14, for example, disclose respective conventional image sensing lenses each including four lenses.